Barrier films

ABSTRACT

The invention concerns composites with excellent barrier properties to gases and water vapor. Such composites can be used, e.g., in foodstuff packaging or as technical membranes. The outstanding barrier effect is achieved by arranging on a substrate material, which, for example, may consist of biodegradable polymers, at least two films. At least one of these films consists of an organic-inorganic hybrid polymer (ORMOCER), at least one further film of a further barrier material or of a substrate material.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention concerns composites of substrate material and,applied on it, a barrier film with a barrier effect to gases and watervapor. The invention also concerns a method for producing thesecomposites. Such composites can be used in packaging, for example, inthe form of foils, panels or shapes and hollow parts, and also fortechnical applications, for example, as membranes or protective filmsfor sensors.

[0003] 2. Summary of Related Art

[0004] Presently, metals, e.g., aluminum or tinplate, glass, polymers,e.g., EVOH or PVDC, and polymers provided with vaporized thin metallicor oxidic films or combinations thereof are generally employed asbarrier materials. As against glass and metals, polymers arecharacterized by their low weight and the small amounts of materialneeded, for which reason they are frequently used especially in thepackaging field. On the other hand, due to their structure andassociated permeability to gases and water vapor, polymers are unsuitedfor applications involving especially high requirements as to barrierproperties. Gaining increasingly in significance, especially due toecological concerns, are the renewable or recycleable polymers. However,they display a comparatively high permeability to gas and presentextremely insufficient barrier properties to water vapor. Therefore,they are barred from many applications.

[0005] Owing to the mostly insufficient barrier effect to gases andwater vapor, polymers are often used in combination with othermaterials. For example, the barrier properties of polymers allowconsiderable improvement by application of thin films of aluminum,aluminum oxide or silicon oxide, but the permeation rates continue to beexcessively high for many applications and can be detected usingconventional measuring techniques (oxygen permeability >0.5 dm³/(m² dbar)). Moreover, renewable polymers show also after coating, as comparedto coated standard polymers such as polyethylene or poly-propylene,permeation rates that are higher by far. Vaporized films being verysensitive to mechanical stresses, it is mostly necessary to laminate thecoated substrates, for example with a foil.

[0006] For some time it has been known (e.g., DE-OS 38 28 098 Al) toproduce scratchproof coating materials by hydrolytic polycondensation ofan organofunctional silane, for example with an aluminum compound, and,as the case may be, with inorganic oxide components. Hybrid polymers (socalled ORMOCERs) synthesized in this fashion possess both inorganic andorganic network structures. The inorganic siliceous network structure isobtained by the sol-gel process (e.g., C. J. Brinker, D. W. Scherer,Sol-Gel-Science; The Physics and Chemistry of Sol-Gel Processing,Academic Press, Inc., New York, 1989) via controlled hydrolysis andcondensation of alkoxy silanes. The siliceous network allows specificmodification by including additionally metal alkoxides in the sol-gelprocess. Additionally, an organic network is produced by polymerizationof organofunctional groups that are introduced in the material by theorganoalkoxy silanes. Reactive methacrylate, epoxy or vinyl groups arepolymerized by thermal or photochemical induction. The ORMOCERs producedin this way can be applied on the medium to be coated by means ofconventional application techniques (spraying, brushing, etc.). Despitesuitable wetting behavior and sound film adhesion, even a composite ofan ORMOCER film and a polymer foil is unable to reduce the highpermeability of many polymers, and notably renewable polymers, to adegree that would be required, e.g., in foodstuff packaging.

OBJECT AND SUMMARY OF THE INVENTION

[0007] Therefore, the objective underlying the present invention is tocoat substrate materials to the effect that they become extensivelyimpermeable to gases and water vapor.

[0008] This objective is satisfied according to the invention bycomposites with the characterizing features set forth in claim 1 and, inprocess-related respects, in claim 21. Favorable embodiments andimprovements of inventional composites derive from the subclaims.

[0009] A composite based on a substrate material on which in accordancewith claim 1 at least two-films are arranged of which at least onebarrier film contains inorganic-organic hybrid polymers (ORMOCER film)while at least one further film of substrate material or other barriermaterial has in comparison with the original substrate material or withsingle-coated substrate material a far lower permeability.

[0010] Inventional composites have a high barrier effect to gases andwater vapor. Surprisingly, even the permeation rates of native polymersnotably allow reduction to an extent such that these prove to beextensively impermeable to gases and water vapor, thus opening new areasof application to native polymers.

[0011] When applying an ORMOCER film 1 μm to 15 μm thick on a substratematerial coated with a barrier film containing a metal and/or metaloxide and/or semiconductor, also the mechanical stability of the filmsapplied first can be drastically improved, in addition to the barriereffect of the composite. Thus, the ORMOCER film assumes at the same timethe function of a mechanical protective film that may make furtherprocess steps, such as lacquering or laminating, superfluous. For thisreason it will mostly prove suitable to apply the ORMOCER film as theconcluding film on the substrate material that has already been coatedotherwise.

[0012] Of course, it is also possible to apply an ORMOCER film directlyon the substrate material. Thereafter, further barrier films (forexample a silicon oxide film) and/or a further substrate material filmmay be applied. For example, the silicon oxide sides of two coatedsubstrate materials or the silicon oxide side of a coated and anuncoated substrate material can be combined on a conventional laminatingsystem with ORMOCER as laminating adhesive.

[0013] Surprisingly, however, already a composite of two substratematerials, for example polymer foils with an ORMOCER barrier filmarranged in between, also possess outstanding barrier properties. TheORMOCER film may also in this case serve as a laminating adhesive.

[0014] While the barrier properties of polymers are by application of abarrier film of silicon oxide of 100 nm thickness improved by a factorof 100, on average, the barrier properties of this composite increaseafter the additional application and curing of an ORMOCER film,surprisingly, once again by a factor of 100. This fact shows whichsignificance attaches exactly to a double-film application.

[0015] Instead of the silicon oxide film, also metal films may be used,for example films of aluminum or other prior-art coating metals and/orsemiconductor films such as silicon film and/or metal oxide films suchas aluminum oxides, magnesium oxides, cerium oxides, hafnium oxides,tantalum oxides, titanium oxides such as titanium dioxide, titanium (3)oxide or titanium monoxide, yttrium oxides or zirconium oxides such aszirconium monoxide, as well as barrier-films containing mixtures ofthese substances. The metal and/or metal oxide and/or semiconductorfilms typically have a thickness of 5 nm to 1000 nm, preferably between20 and 150 nm.

[0016] All of the polymers (e.g., polyamide, polyethylene, polyproyleneor polyester) lend themselves as substrate materials for coatingsaccording to the invention. Especially applicable as substrate materialsare biologically decomposable polymers and particularly native polymers(cellophane, proteinaceous or starchy polymers) with an inherently lowbarrier effect. Also paper, cardboard, coated paper or coated cardboardare suited as substrate materials. Particularly pronounced improvementsin view of gas and water vapor permeability are achievable with theinventional coating in the case of thin substrate mainly (for examplefoils) having thicknesses in the range of about 5 μm to 2 mm. Inaddition to foils, however, also panels, shapes, hollow articles,membranes or protective films for sensors are suited as substratematerials.

[0017] Sealability of the composites can be guaranteed with the use ofsealable substrate films or by application of sealable films on thecomposites. An example would be a copolymer film coextruded onpolypropylene. Sealability is of great significance especially infoodstuff packaging. Also the use of oriented polymers, for exampleaxially or biaxially oriented polypropylene, has proved to be favorable.

[0018] Inventionally coated plastics, notably native polymers, open forthemselves a great many new areas of application which so far wereunavailable to plastics (for example foodstuff preserves). Metal orglass could in many areas be substituted by plastics coated in thisfashion, which means drastic weight savings. Furthermore, plasticscoated in this fashion allow the manufacture of barrier materials which,unlike metals, are transparent. Possible also is the realization of asealable, nearly varietally pure barrier composite (refer to exemplaryembodiment 5).

[0019] The barrier properties of the ORMOCER allow specific adjustmentby kind and share of the organic and inorganic network as well as viathe network converters. Both the wetting behavior and film adhesion aswell as the barrier properties can be optimized in this way. Thethickness of the applied ORMOCER film ranges typically from 1 μm to 15μm. The invention covers all of the ORMOCERs known so far in the priorart. Express reference is made to the disclosure content of DE-OS 38 28098 as well as DE 43 03 570.

[0020] The further, inventional addition of functionalized SiO₂particles, which in the ORMOCER synthesis are worked in and covalentlybound to the organic network, leads to a higher density of the inorganicnetwork. Instead of SiO₂ particles, also other particles may be used,for example functionalized Al₂O₃ particles. The barrier properties ofthe composite allow in this way still further improvement.

[0021] Inventional composites with barrier properties can be produced byapplying at least two films on a substrate material, with at least oneof these films being a barrier film containing ORMOCERs, which film isapplied by brushing, spraying, rolling, centrifugal or doctor processesand subsequently cured by heat and/or photochemical induction and/orthermal induction, and with at least one further film of another barriermaterial or substrate material being applied before or after applicationof the at least one ORMOCER film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Further details, characteristics and advantages of the presentinvention derive from the following exemplary embodiments and with theaid of the drawing figures, showing in:

[0023]FIG. 1, a simplified illustration of an amino-functionalized SiO₂particle;

[0024]FIG. 2, an exemplary embodiment of a polymer foil with a vaporizedSiO_(x) film and an ORMOCER protective film;

[0025]FIG. 3, an exemplary embodiment of a sealable composite consistingof two polymer foils with vaporized SiO_(x) films and an ORMOCER film aslaminating adhesive;

[0026]FIG. 4, an exemplary embodiment of a foil composite of two polymerfoils between which an ORMOCER film is disposed as laminating adhesive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] The following describes the exemplary composition of two suitableORMOCER lacquers. Coating material 1   40 mol % TMOS 12.5 mol % Al(OBu^(S))₃ 32.5 mol % GLYMO   10 mol% Zr (OPr)₄   5 mol % AMEO Thislacquer system is cured thermally at 130° C. Coating material 2 70 mol %MEMO 15 mol % methacrylic acid 15 mol % Zr (OPr)₄ This lacquer system iscured by photochemical or thermal induction.

[0028] Abbreviations:

[0029] TMO Stetramethoxy silane

[0030] GLYMO 3-glycidoxypropyltrimethoxy silane

[0031] AMEO 3-aminopropyltriethoxy silane

[0032] MEMO 3-methacryloxypropyltrimethoxy silane

[0033] Al(OBu³)₃ aluminum trisecondary butylate

[0034] Zr(OPr)₄ zirconium tetrapropylate

[0035] BOPP biaxially oriented polypropylene

[0036] PETP polyethylene terephthalate

[0037] To improve the barrier properties, approximately 1 mass-% ofamino-functionalized (FIG. 1) or methacrylate-functionalized SiO₂particles by the firm Degussa (Aerosil 200) may be incorporatedadditionally in both systems during the lacquer synthesis.

[0038] Several exemplary embodiments of inventional composites withbarrier properties are described hereafter. The silicon oxide films areapplied, e.g., by vaporization of silicon monoxide or by means of plasmaCVD (chemical vapor deposition). ORMOCERs may be applied by conventionallacquering processes such as spraying, brushing, rolling orcentrifuging; in the exemplary embodiments, coating may be carried outusing a raster roll. The applied ORMOCER lacquers are cured preferablyin-line, for example by heat or photochemical induction.

[0039] Exemplary Embodiment 1

[0040] To begin with, an SiO_(x) film about 100 nm thick is vaporized ona sealable BOPP foil of about 20 μm thickness. Next, the SiO_(x) film iscoated over with about 3 g/m² ORMOCER and cured (FIG. 2). The startingfoil has at 23° C. and about 75% relative humidity an oxygenpermeability of about 30 cm³/(m² d bar). The oxygen permeability of thefoil coated additionally with ORMOCER is <1 cm³/(m² d bar). The foil canbe used as a sealable high-barrier packaging foil.

[0041] Exemplary Embodiment 2

[0042] To begin with, an SiO_(x) film about 100 nm thick is vaporized ona PETP foil of about 12 μm thickness. Next, the SiO_(x) film is coatedover with about 3 g/m² ORMOCER and cured. The starting foil has at 23°C. and about 75% relative humidity an oxygen permeability of about 2cm³/(m² d bar). The oxygen permeability of the foil coated additionallywith ORMOCER is no longer detectable with commercially availablepermeability measuring apparatuses, that is, it amounts to <0.05 cm³ (m²d bar). Upon application of a sealing lacquer or after laminating, e.g.,to a polyethylene foil, the foil could be used as high-barrier packagingfoil.

[0043] Exemplary Embodiment 3

[0044] To begin with, an SiO_(x) film about 100 nm thick is vaporized ona cellophane foil of about 20 μm thickness. Next, the SiO_(x) film iscoated over with about 3 g/m² ORMOCER and cured (FIG. 2). The startingfoil has at 23° C. and 0 to 85% relative humidity gradient a water vaporpermeability of about 20 g/(m² d). The water vapor permeability of thefoil coated additionally with ORMOCER amounts to approximately 0.5 g/(m²d). Hence, the water vapor permeability is so low that, unlike all otherfoils of renewable raw materials, the foil can be used also forpackaging very moisture-sensitive goods.

[0045] Exemplary Embodiment 4

[0046] The coated sides of two foils (a PEPT foil 12 μm thick and anLDPE foil 60 μm thick) vaporized with SiO_(x) are glued on aconventional laminating system (FIG. 3) with ORMOCER serving aslaminating adhesive. The resulting composite has an oxygen permeabilityof <0.05 cm³ (m² d bar), is sealable and can be used, e.g., forfoodstuff packaging.

[0047] To realize a barrier composite with good barrier properties it issufficient to glue (FIG. 4) uncoated polymer foil, for example of PP, PEor PET, using ORMOCERs as laminating adhesive. To that end, for examplea PE foil 15 μm thick is on a conventional laminating system glued to aPETP foil of 15 μm thickness by means of ORMOCER.

[0048] Exemplary Embodiment 5

[0049] The coated sides of two BOPP foils (one foil of PP-homopolymerand the other a sealable triple-film foil) vaporized with SiO_(x) each20 μm thick are glued on a conventional laminating system using ORMOCERas laminating adhesive. The resulting composite is sealable and nearlyvarietally clean, that is, apart from the thin barrier films it containsonly polypropylene as polymer.

[0050] Of course, inventional composites are not limited to foils. Alsopanels, shapes and hollow articles, membranes, protective films forsensors or other mediums, which should have a good barrier effect togases and water vapor, lend themselves as substrate mediums for acoating according to the invention.

[0051] In addition to polymers, inventional barrier films may be appliedalso on cardboard, paper, coated cardboard or coated paper. For example,an ORMOCER primer may be applied first on cardboard or paper, followedby a metal or metal oxide film. Suitable as mechanical protective filmon top of these would be again a concluding ORMOCER film. Paperlaminated with an ORMOCER film on the vaporized side of a substrate foilmay be used as well.

1. Composite of substrate material and at least one film (barrier film)containing a barrier material, characterized in that at least two filmsare arranged on the substrate material, with at least one barrier filmcontaining inorganic-organic hybrid polymers (ORMOCER film) and at leastone further film containing substrate material or another barriermaterial.
 2. Composite according to claim 1, characterized in that on atleast one ORMOCER film disposed on the substrate material there isarranged at least one further barrier film.
 3. Composite according toclaim 1, characterized in that on at least one further barrier filmdisposed on the substrate material there is arranged at least oneORMOCER film.
 4. Composite according to claim 1, characterized in thatleast one ORMOCER film is arranged between two substrate materials. 5.Composite according to claim 4, characterized in that at least oneORMOCER film is arranged as laminating film between two substratematerials.
 6. Composite according to at least one of the precedingclaims, characterized in that the composite comprises in addition to atleast one ORMOCER film at least one further barrier film that contains ametal and/or a metal oxide and/or a semiconductor.
 7. Compositeaccording to at least one of the preceding claims, characterized in thatthe system comprises besides at least one ORMOCER film at least onefurther barrier film that contains aluminum oxides, magnesium oxides,cerium oxides, hafnium oxides, tantalum oxides, silicon oxides such assilicon monoxide or silicon dioxide, titanium oxides such as titaniumdioxide, titanium (3) oxide or titanium monoxide, yttrium oxides,zirconium oxides such as zirconium monoxide, or mixtures thereof. 8.Composite according to claim 6 or 7, characterized in that the barrierfilm containing a metal and/or a metal oxide and/or a semiconductor hasa thickness between 5 nm and 1000 nm.
 9. Composite according to at leastone of the preceding claims, characterized in that the ORMOCER film hasa thickness between 1 μm and 15 μm.
 10. Composite according to at leastone of the preceding claims, characterized in that functionalized SiO₂particles or functionalized Al₂O₃ particles are incorporated in theORMOCER film.
 11. Composite according to at least one of the precedingclaims, characterized in that the substrate material consists of paper,cardboard, coated paper or coated cardboard.
 12. Composite according toat least one of the claims 1 through 10, characterized in that thesubstrate material consists of polymer material.
 13. Composite accordingto at least one of the claims 1 through 10, characterized in that thesubstrate material consists of polyamide, polyethylene, polypropylene orpolyester.
 14. Composite according to at least one of the claims 1through 10, characterized in that the substrate material consists of atleast one biologically degradable polymer.
 15. Composite according to atleast one of the claims 1 through 10, characterized in that thesubstrate material consists of at least one native polymer. 16.Composite according to at least one of the claims 1 through 10,characterized in that the substrate material consists of cellophane, astarchy or a proteinaceous material.
 17. Composite according to at leastone of the preceding claims, characterized in that the substratematerial is on hand as foils, panels, shapes, hollow articles, membranesor protective films for sensors.
 18. Composite according to one of theclaims 12 through 16, characterized in that the substrate material is afoil with a thickness between 5 μm and 2 mm.
 19. Composite according toclaim 18, characterized in that the substrate material consists of anoriented polymer.
 20. Composite according to at least one of thepreceding claims, characterized in that the substrate material issealable and/or provided with a sealable film.
 21. Method for themanufacture of composites with barrier properties, characterized in thatat least two films are applied on at, least one substrate material, withat least one of said films being a barrier film containing ORMOCERs,said barrier film being applied by brushing, spraying, rolling,centrifugal or doctor processes and subsequently cured by heat and/orphotochemical induction and/or thermal induction, and with at least onefurther film of another barrier material or of a substrate materialbeing applied before or after application of the at least one ORMOCERfilm.